Off-flavor has been identified as one of the most serious problems in the catfish industry. Off-flavor can render fish unpalatable, and thus delay the harvesting and marketing of commercially produced fish such as channel catfish. Losses due to off-flavor often run into the thousands of dollars for each incidence of the problem, and annual losses exceed $100 million.
Off-flavor is a complex phenomenon that is related to the absorption of compounds that are produced by cyanobacteria, algae, and actinomycetes. Geosmin (trans-1,10-dimethyl-trans-9-decalol) and 2-methylisoborneol (MIB) are produced by cyanobacteria and actinomycetes, and these two compounds have been shown to cause off-flavor in channel catfish. Although the roles of the various organisms and compounds are not completely understood, most geosmin off-flavor in commercially produced channel catfish has been attributed to species of Anabaena, while MIB off-flavor has been linked to a planktonic species identified as Oscillatoria cf. chalybea.
The concept of controlling off-flavor by management of cyanobacteria has been proposed (Van der Ploeg, M.; Proc. World Aquaculture Soc., p. 71, 1994 (Abst.)), but no selective control measures have been developed. Conventional control practices include application of broad-spectrum algicides, such as copper sulfate or diurion [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. The introduction of certain chemical agents to fresh water reservoirs or fisheries for the reduction, control or elimination of off-flavor can be undesirable. Alternative approaches not requiring the addition of chemical agents are preferred but almost nonexistent.
Viruses and microorganisms are involved in the population dynamics of cyanobacteria in nature, but there are no reports of attempts to use biological control technology to manage cyanobacteria in channel catfish ponds.
Thus, there remains a significant need for the development of alternate strategies for the reduction of off-flavor in fresh water supplies and in fish harvested from fresh water nurseries.